You could try a variety of ways, there's no real hard and fast way of doing it. For example, my daughter had formula until she was almost 3 (!) and then switched straight onto cow's milk and has always had it warm. My son has had cow's milk since he was just over 1 year old and has it straight from the fridge! She drinks her milk from a cup, he still has a bottle (he's just over 2 years old).
Some people advocate switching gradually - so half formula, half cow's milk - and this can minimise any problems with changing over, like diarrhoea or just general problems with the taste being different to them. We did try this with our son when he got severe diarrhoea after starting cow's milk, but ended up on lactose-free milk which was fine.
Personally, I think the more subtle approach is best, so mixing formula and cow's milk and still giving it in a bottle. You may have to play about with the temperature as formula is kind of slightly warmer than room temperature in general.